An EVOH having an excellent oxygen gas barrier property is widely used as a material for a variety of packages and bottles. The EVOH is produced by copolymerizing vinyl acetate and ethylene and saponifying the resulting ethylene-vinyl acetate copolymer in the presence of an alkaline catalyst with the use of methanol as a solvent. The EVOH resulting from the saponification is provided in the form of a methanol solution under heating and pressure. A part of methanol in the EVOH methanol solution is replaced with water. The resulting EVOH water/methanol solution can be stably handled under ordinary temperature and ordinary pressure conditions.
The replacement of the EVOH solution with water is industrially continuously carried out in a tower vessel. Patent Documents 1 and 2, for example, disclose methods in which an EVOH methanol solution supplied from an upper portion of a plate tower or a packed tower is kept in counter-flow contact with water vapor supplied from a lower portion of the tower for the replacement of a part of methanol in the solution with water. In the methods disclosed in Patent Documents 1 and 2, an excess portion of the water vapor and methanol vapor resulting from the replacement with water are extracted from a tower top of the tower vessel to be introduced into a condenser, and liquefied in the condenser.
Patent Document 1: JP-A-2002-121216
Patent Document 2: JP-A-2002-121290